POS0143 TISSUE RESIDENT MEMORY AND CYTOTOXIC T CELLS ARE CLONALLY EXPANDED IN THE MUSCLE OF PATIENTS WITH IDIOPATHIC INFLAMMATORY MYOPATHIES
Authors: A. S. Galindo-Feria, A. Argyriou, B. Horuluoglu, J. S. Díaz-Boada, A. Notarnicola, L. Dani, A. Van Vollenhoven, D. Ramsköld, I. Nennesmo, M. Dastmalchi, I. E. Lundberg, L. M. Diaz-Gallo, K. Chemin
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Idiopathic inflammatory myopathies (IIM) are rare autoimmune systemic diseases characterized by muscle weakness and presence of muscle-infiltrating T cells. IIM represent a clinical challenge due to heterogeneity of symptoms and variability of response to immunosuppressive treatment. <h3>Objectives</h3> We aimed to explore the mechanisms involved in T cell migration and persistence in the muscle tissues of patients with IIM. <h3>Methods</h3> We performed single-cell RNA sequencing on muscle-infiltrating and peripheral blood (PB) memory T cells from patients with recently diagnosed IIM (n=7) from the Rheumatology Clinic, Karolinska University Hospital. Briefly, after enzymatic digestion of fresh muscle tissue, we single-cell sorted T cells from seven patients who also presented muscle infiltrates by histopathological analysis: immune-mediated necrotizing myopathy (IMNM) n=2; inclusion body myositis (IBM) n=2; dermatomyositis (DM) n=1; and antisynthetase syndrome (ASyS) n=1 and a non-inflammatory myopathy. Muscle T cells were sorted based on the co-expression of CD45 and CD3, whereas PB memory T cells were sorted based on the exclusion of naïve CD45RA<sup>+</sup>CCR7<sup>+</sup> CD3<sup>+</sup> T cells. We also aligned the TCR sequences. We had access to additional muscle and PB samples from two patients after immunosuppressive treatment. Description of the methodology is presented in Figure 1. <h3>Results</h3> After quality control, filtering, and normalization processes of the gene expression matrix, the total number of T cells recovered from the analysis was 2,844, out of which 1,427 were isolated from the muscle and 1,417 cells from PB. Muscle and PB T cells grouped separately indicating different gene signature. Three different clusters containing muscle T cells (cluster 1), PB CD8+ T cells (cluster 2) and PB CD4+ T cells (cluster 3) were identified, showing different transcriptomic signature between muscle and PB T cells. After unsupervised clustering of gene expression, we identified 15 distinct T-cell clusters annotated based on differentially expressed genes and visualized by UMAP. We found enrichment in the muscle compartment compared to blood for the following clusters: tissue-resident memory (T<sub>RM</sub>) T cells, muscle central memory (CM) CD4+ T cells, muscle effector memory (EM)T cells, EGR1hi and T<sub>RM</sub> genes, and Tregs. All clusters were present in all patients except for the Tregs cluster, which was not detected in the patient with ASyS. A distinct signature between muscle T cells and blood memory T cells was revealed by the differential expression of genes involved in transcription, migration, dephosphorylation, cell cycle, metabolism, cytoskeleton and signalling. Additionally, expanded T-cell clones were observed in all patients' muscle tissue, ranging between 20-50% of all TCR sequences. We could identify expanded T-cell clones persisting at follow-up in the muscle of one patient with IMNM and another with ASyS after immunosuppressive treatment. <h3>Conclusion</h3> Our study reveals a muscle T-cell signature in patients with IIM and a transcriptomic map to identify possible novel therapeutic targets in IIM, where muscle-infiltrating T cells are predominantly composed of cytotoxic, effector memory, tissue-resident, proliferating and regulatory T cells. The expression of tissue-resident memory (T<sub>RM</sub>) receptors and the presence of clonally expanded T-cell clones in the muscle of all patients with IIM imply the role of these cells in disease pathogenesis. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Angeles Shunashy Galindo-Feria: None declared, Alexandra Argyriou: None declared, Begum Horuluoglu: None declared, Juan Sebastian Díaz-Boada: None declared, Antonella Notarnicola: None declared, Lara Dani: None declared, Annika van Vollenhoven: None declared, Daniel Ramsköld: None declared, Inger Nennesmo: None declared, Maryam Dastmalchi: None declared, Ingrid E. Lundberg Shareholder of: Stock shares in Roche and Novartis., Paid instructor for: Has been serving on the advisory board for Corbus Pharmaceutical, EMD Serono. Research &amp; Development Institute, Argenx, Octapharma, Pfizer, Kezaar, Orphazyme and Janssen, Consultant of: Corbus Pharmaceuticals, Inc, Grant/research support from: Astra Zeneca, Lina M. Diaz-Gallo: None declared, Karine Chemin: None declared.